Focusing system, interchangeable lens, and image-capturing device

ABSTRACT

A focusing system includes a first drive unit for driving a first focus lens along the optical axis, a second drive unit for driving a second focus lens along the optical axis, a determining unit for periodically detecting a focus state of a subject image formed via the optical system and determining a focus position of the optical system based on the detected result, and a control unit for controlling the first and second drive units according to a result of determining the focus position of the optical system by the determining unit. The control unit controls the second drive unit to drive the second focus lens independently of the first focus lens, in the focus operation.

TECHNICAL FIELD

The present invention relates to a focusing system that has an opticalsystem including a plurality of focus lens groups and is capable ofperforming automatic focus detection, and an interchangeable lens and animage-capturing device equipped with such a focusing system.

BACKGROUND ART

In camera systems, miniaturization of lens barrels is highly demandedand heightening of an autofocus speed is required. With a focusingsystem composed of a plurality of focus lens groups, a stroke length ismade shorter than that with the focusing system composed of a singlefocus lens group. Thus, an entire length of a lens barrel can beshortened and an autofocus speed is heightened. Particularly in macrolenses, a deterioration in a performance of macro regions can beimproved.

For example, a lens barrel described in Patent Document 1 has aplurality of focus lens groups, and one motor drives the plurality offocus lens groups using a cam mechanism.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP 2006-154473 A

DISCLOSURE OF INVENTION Problem to be solved by the Invention

A focusing system composed of a plurality of focus lens groups arecomposed of a main group focus lens to be driven to scan a focusposition, and a sub group of focus lens to be driven cooperatively tosecure focus accuracy for the scanning of the main group focus lens. Insuch focusing systems including a plurality of drive systems, noises maybe generated due to drive and tone occasionally may change.

Particularly, during recording of moving images, the main group focuslens is always driven slightly to continuously scan the focus position.Since sound recording is normally carried out in the recording of movingimages, the generation of noises and the change in the tone cause adeterioration in sound quality, thereby resulting in a problem.

The present invention is devised in view of the above problem, and itsobject is to solve the problem of a sound generated by drive of afocusing system composed of a plurality of focus lens groups.

Means for Solving the Problem

In a first aspect, a focusing system is provided which has an opticalsystem including first and second focus lenses for regulating a focusstate of a subject image, the focusing system being capable ofperforming a focus operation for automatically controlling the first andsecond focus lenses on a focus position. The focusing system includes afirst drive unit for driving the first focus lens along the opticalaxis, a second drive unit for driving the second focus lens along theoptical axis, a determining unit for periodically detecting a focusstate of the subject image formed via the optical system and determininga focus position of the optical system based on the detected result inthe focus operation, and a control unit for controlling the first andsecond drive unit according to a result of determining the focusposition of the optical system by the determining unit. The control unitcontrols the second drive unit to drive the second focus lensindependently of the first focus lens in the focus operation.

In a second aspect, for example, the control unit may control the firstdrive unit to drive the first focus lens slightly forward and backwardalong the optical axis and control the second drive unit to drive thesecond focus lens independently of the first focus lens, in order todetect a focus state of the subject image by the determining unit in thefocus operation.

Specifically, the control unit may control the first drive unit to drivethe first focus lens slightly forward and backward along the opticalaxis and control the second drive unit to drive the second focus lens ata constant speed, in order to determine the focus position of theoptical system by the determining unit.

Alternatively, when a center position of the first focus lens in drivingslightly forward and backward shifts, the control unit may control thesecond drive unit to drive the second focus lens at a constant speed.

Alternatively, when the center position of the first focus lens indriving slightly forward and backward shifts and a difference between atracking position of the second focus lens with respect to a currentposition of the first focus lens and a current position of the secondfocus lens is equal to or more than a predetermined value, the controlunit may control the second drive unit to drive the second focus lens ata constant speed.

In a third aspect, the control unit may control the first drive unit todrive the first focus lens to set the subject image in an in-focus stateand control the second drive unit to drive the second focus lensindependently of the first focus lens based on the determined result ofthe determining unit in the focus operation.

Specifically, the control unit may control the first drive unit to drivethe first focus lens to set the subject image in the in-focus state andcontrol the second drive unit to drive the second focus lensindependently of the first focus lens based on the determined result ofthe determining unit in the focus operation.

Alternatively, the control unit may control the second drive unit todrive the second focus lens at a constant speed until the determiningunit determines the focus position of the optical system.

Alternatively, the control unit may control the second drive unit tostop the second focus lens until the determining unit determines thefocus position of the optical system.

Alternatively, when a difference between a tracking position of thesecond focus lens with respect to a current position of the first focuslens and a current position of the second focus lens is not less than apredetermined value, the control unit may control the second drive unitto drive the second focus lens.

Alternatively, the determining unit may firstly detect the focusposition, and then secondly determine the focus position based on thedetected result.

In this case, when driving the first focus lens to secondly determinethe focus position after the first focus lens passes through the focusposition which is firstly determined as a focus position, the controlunit may control the second drive unit to transfer the second focus lensaccording to the tracking position of the second focus lens with respectto the current position of the first focus lens.

Alternatively, when driving the first focus lens to secondly determinethe focus position after the first focus lens passes through the focusposition which is firstly determined as a focus position, the controlunit may not start driving of the first focus lens until the secondfocus lens reaches the tracking position when the difference between thetracking position of the second focus lens with respect to the currentposition of the first focus lens and the current position of the secondfocus lens is not less than the predetermined value.

Alternatively, after the determining unit detects a position where thesubject image is in-focus, the control unit may control the second driveunit to drive the second focus lens at the constant speed to set thesubject image in the in-focus state.

In a fourth aspect, an image-capturing device is provided, whichincludes the focusing system having the above configuration.

In a fifth aspect, an interchangeable lens mountable to a camera body isprovided, which includes the focusing system having the aboveconfiguration.

Effect of the Invention

According to the above configuration, in the focusing system composed ofthe focus lens groups, the second focus lens is driven independently ofthe first focus lens at the time of the focus operation. As a result,the second focus lens can be driven at the constant speed or stopped inthe focus operation, thereby preventing noises and a change in tonecaused by a change in a drive speed of the second focus lens. As aresult, noise reduction and quality of recorded sounds can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of configuration of a digital camera.

FIG. 2 is a block diagram of a camera body.

FIG. 3 is a perspective view of the digital camera.

FIG. 4A is a top view illustrating the camera body, and FIG. 4B is arear view illustrating the camera body.

FIG. 5 is a cross-sectional view illustrating an interchangeable lensunit (an in-focus state at infinite end).

FIG. 6 is a cross-sectional view illustrating the interchangeable lens(an in-focus state at infinite end).

FIG. 7 is an exploded perspective view illustrating a second lens groupunit.

FIG. 8 is an exploded perspective view illustrating a fourth lens groupunit.

FIG. 9 is an exploded perspective view illustrating a fifth lens groupunit.

FIG. 10A is a diagram of configuration of an optical system in thein-focus state at a infinite end, and FIG. 10B is a diagram ofconfiguration of an optical system in an in-focus state at a nearestend.

FIG. 11 is a diagram illustrating a positional relationship of therespective lens groups at the time of focusing (tracking curves).

FIG. 12A is an explanatory diagram illustrating focus detection in ahill climbing system (tracking drive).

FIG. 12B is an explanatory diagram illustrating the focus detection inthe hill climbing system (tracking drive).

FIG. 13 is an explanatory diagram illustrating a focus detection drivingmethod in the hill climbing system according to a first embodiment.

FIG. 14 is an explanatory diagram illustrating the focus detectiondriving method in the hill climbing system according to a secondembodiment.

FIG. 15 is an explanatory diagram illustrating the focus detection in awobbling operation (tracking drive).

FIG. 16 is an explanatory diagram illustrating the focus detectiondriving method using the wobbling according to a third embodiment.

FIG. 17 is an explanatory diagram illustrating the focus detectiondriving method using the wobbling according to a fourth embodiment.

FIG. 18 is an explanatory diagram illustrating the focus detectiondriving method using the wobbling according to the fourth embodiment.

FIG. 19 is a flowchart illustrating the focus detection driving methodin the hill climbing system according to the second embodiment.

FIG. 20 is a flowchart illustrating the focus detection driving methodusing the wobbling according to the fourth embodiment.

FIG. 21 is an explanatory diagram illustrating the focus detectiondriving method in the hill climbing system according to a fifthembodiment.

FIG. 22 is a flowchart illustrating the focus detection driving methodin the hill climbing system according to the fifth embodiment.

MODE FOR CARRYING OUT THE INVENTION

First Embodiment

A configuration and an operation of a digital camera according to afirst embodiment are described below with reference to accompanyingdrawings.

1. Configuration

1-1. Entire Configuration

An outline of a digital camera 1 is described with reference to FIG. 1.FIG. 1 is a schematic diagram illustrating a configuration of thedigital camera 1. As shown in FIG. 1, the digital camera 1 (one exampleof an image-capturing device), that is an interchangeable lens typedigital camera, has a camera body 3 and a detachable interchangeablelens unit 2 attached to the camera body 3. The interchangeable lens unit2 is attached to the camera body 3 via a lens mount 95 and a body mount4 provided to a front surface of the camera body 3.

FIG. 2 is a block diagram illustrating a configuration of the camerabody 3. FIG. 3 is a schematic perspective view of the digital camera 1.FIG. 4A is a top view illustrating the camera body 3, and FIG. 4B is arear view illustrating the camera body 3. FIGS. 5 to 6 are schematiccross-sectional views illustrating the interchangeable lens unit 2 thatis cut along different planes. FIG. 7 is an exploded perspective viewillustrating a first focus regulating unit 72. FIG. 8 is an explodedperspective view illustrating a second focus regulating unit 73. FIG. 9is an exploded perspective view illustrating a third focus regulatingunit 74. FIGS. 10A and 10B are diagrams illustrating a configuration ofan optical system L. FIG. 10A illustrates an in-focus state at aninfinite end, and FIG. 10B illustrates an in-focus state at a nearestend. FIG. 11 illustrates distances from imaging sensors 11 of respectivelens groups at the time of focusing.

In the first embodiment, a three-dimensional orthogonal coordinatesystem is set in the digital camera 1. An optical axis AZ of the opticalsystem L (described later) matches with a Z-axis direction. The X-axisdirection matches with a horizontal direction of the digital camera 1held for shooting a portrait-oriented image. A Y-axis direction matcheswith a vertical direction of the digital camera 1 which is held forshooting a landscape-oriented image. Further, in the followingdescription, “front” means a side of a subject of the digital camera 1(a positive side in the Z-axis direction), and “rear” means a sideopposite to the subject side of the digital camera 1 (on a side of theimaging sensor, a negative side in a Z-axis direction).

1-2. Interchangeable Lens Unit

A schematic structure of the interchangeable lens unit 2 is describedwith reference to FIGS. 1 to 11. As shown in FIG. 1, the interchangeablelens unit 2 has the optical system L, a lens supporting mechanism 71 forsupporting the optical system L, the first focus regulating unit 72, thesecond focus regulating unit 73, a third focus regulating unit 74, adiaphragm regulating unit 75, a shake correcting unit 76, and a lensmicrocomputer 40.

The optical system L forms an optical image of a subject. The opticalsystem L is mainly composed of six lens groups. Concretely, as shown inFIGS. 10A and 10B, the optical system L has a first lens group G1 havinga positive refractive power, a second lens group G2 having a negativerefractive power, a third lens group G3 having a positive refractivepower, a fourth lens group G4 having a positive refractive power, afifth lens group G5 having a negative refractive power, and a sixth lensgroup G6 having a positive refractive power.

The first lens group G1 includes a first lens L1, a second lens L2, anda third lens L3. The second lens group G2 is a focus lens group, andincludes a fourth lens L4, a fifth lens L5 and a sixth lens L6. Thethird lens group G3 is a shake correcting lens group, and includes aseventh lens L7. The fourth lens group G4 is a focus lens group andincludes an eighth lens L8, a ninth lens L9 and a tenth lens L10. Thefifth lens group G5 is a focus lens group and includes an eleventh lensL11. The sixth lens group G6 includes a twelfth lens L12 and athirteenth lens L13.

That is to say, in the optical system L, the lens groups G2, G4 and G5are focus lens groups. The focus lens groups G2, G4 and G5 transferalong the optical axis to change an imaging distance (object distance).

As shown in FIGS. 10A, 10B and 11, in focusing from the in-focus stateat an infinite end to the in-focus state at a nearest-end, the secondlens group G2 transfers to the imaging sensor 11 along the optical axisAZ, and the fourth lens group G4 and the fifth lens group G5 transfer tothe subject side along the optical axis AZ.

Further, in order to repress a shake of an optical image caused by amovement of the digital camera 1, the seventh lens L7 transfers to twodirections perpendicular to the optical axis AZ.

FIG. 11 is a diagram illustrating tracking curves of the respectivefocus lens groups according to the first embodiment. As shown in FIG.11, when the respective focus lens groups transfer from the in-focusstate at the infinite end to the in-focus state at the nearest end, theyestablish a predetermined positional relationship.

In FIGS. 1, 5 and 6, the lens supporting mechanism 71 is a mechanism forfixing or movably supporting the respective lens groups G1 to G6 of theoptical system L, and has a lens mount 95, a fixing frame 50, a guidepole supporting frame 51, a first lens group supporting frame 52, asecond lens group supporting frame 53, a third lens group supportingframe 54, a diaphragm unit 62, a fourth lens group supporting frame 55,a fifth lens group supporting frame 56, a sixth lens group supportingframe 57, and a focus ring unit 88.

The lens mount 95 is a portion that is attached to the body mount 4 ofthe camera body 3, and has a lens side contact point 91.

The fixing frame 50 supports a front frame 61, the first lens groupsupporting frame 52, the diaphragm unit 62, a first focus motor 63 and asecond focus motor 64. The fixing frame 50 further supports front endportions of four guide poles 63 b, 63 c, 64 b and 64 c extending to theZ axis direction, and is fixed to the guide pole supporting frame 51.The first focus motor 63 and the second focus motor 64 are, for example,stepping motors.

The guide pole supporting frame 51 supports the sixth lens groupsupporting frame 57, guide poles 65 c and 65 b and a third focus motor65, and supports rear end portions of the four guide poles 63 b, 63 c,64 b and 64 c. The guide pole supporting frame 51 is fixed to the lensmount 95. The third focus motor 65 is, for example, a stepping motor.

The front frame 61 is fixed to the fixing frame 50, and a female threadportion 61 a for mounting an optical filter, such as a polarizationfilter or a protective filter, and a conversion lens is formed on itsfront end.

The first lens group supporting frame 52 is fixed to the fixing frame 50and supports the first lens group G1.

The second lens group supporting frame 53 supports the second lens groupG2, and has a bearing section 53 a, a whirl stop section 53 b, a racksupporting section 53 c and a protrusion 53 d. The guide pole 63 b isinserted into the bearing section 53 a, the guide pole 63 c is insertedinto the whirl stop section 53 b, and the second lens group supportingframe 53 is supported movably to the Z axis direction in a state thatits rotation about the optical axis AZ is regulated. The rack supportingsection 53 c supports a first rack 58 integrally with the Z axisdirection and movably and rotatably. The protrusion 53 d is a portionfor detecting an original point of the second lens group G2, and isprovided to a position where it can pass through a detection region of afirst photosensor 66. The first rack 58 has a plurality of teeth (notshown), and these teeth are geared with a lead screw 63 a of the firstfocus motor 63.

The third lens group supporting frame 53 supports the third lens groupG3. The third lens group supporting frame 54 is supported movably to twodirections perpendicular to the optical axis AZ.

The fourth lens group supporting frame 55 supports the fourth lens groupG4, and has a bearing section 55 a, a whirl stop section 55 b, a racksupporting section 55 c and a protrusion 55 d. The guide pole 64 b isinserted into the bearing section 55 a, and the guide pole 64 c isinserted into the whirl stop section 55 b. The fourth lens groupsupporting frame 55 is supported movably to the Z axis direction in astate that its rotation about the optical axis ZA is regulated. The racksupporting section 55 c supports a second rack 59 integrally, movablyand rotatably in the Z axis direction. The protrusion 55 d is a portionfor detecting an original point of the fourth lens group G4, and isprovided to a position where it can pass through a detection region of asecond photosensor 67. The second rack 59 has a plurality of teeth (notshown), and these teeth are geared with a lead screw 64 a of the secondfocus motor 64.

The fifth lens group supporting frame 56 supports the fifth lens groupG5, and has a bearing section 56 a, a whirl stop section 56 b, a racksupporting section 56 c and a protrusion 56 d. The guide pole 65 b isinserted into the bearing section 56 a, and the guide pole 65 c isinserted into the whirl stop section 56 b. The fifth lens groupsupporting frame 56 is supported movably in the Z axis direction in astate that its rotation about the optical axis AZ is regulated. The racksupporting section 56 c supports a third rack 60 integrally, movably androtatably in the Z axis direction. The protrusion 56 d is a portion fordetecting an original point of the fifth lens group G5, and is providedto a position where it can pass through a detection region of a thirdphotosensor 68. The third rack 60 has a plurality of teeth (not shown),and these teeth are geared with a lead screw 65 a of the third focusmotor 65. The sixth lens group supporting frame 57 supports the sixthlens group G6, and is fixed to the guide pole supporting frame 51.

The focus ring unit 88 has a focus ring 89, a focus ring angle detectingsection 90 for detecting a rotation angle of the focus ring 89. Thefocus ring 89 has a cylindrical shape, and is supported rotatably aboutthe optical axis AZ by the fixing frame 50 and the front frame 61 in astate its transfer in the Z axis direction is regulated. The rotationangle and the rotation direction of the focus ring 89 can be detected bythe focus ring angle detecting section 90. For example, the focus ringangle detecting section 90 has two photosensors (not shown). The focusring 89 has a plurality of protrusions 89 a that is arranged at equalintervals in the rotation direction and protrudes to the Z axisdirection. The respective photosensors have a light emitting section(not shown) and a light receiving section (not shown). The protrusions89 a pass between the light emitting section and the light receivingsection so that the photosensors can detect the rotation angle and therotation direction of the focus ring 89. The focus ring 89 may haveanother structure such as a movable lever.

The first focus regulating unit 72 has the first focus motor 63, a focusdrive controller 41, and the first photosensor 66. The first focus motor63 is on a side closer to an imaging surface than the diaphragm unit 62,and is fixed to the fixing frame 50. The first focus motor 63 drives thesecond lens group supporting frame 53 to the Z axis direction. The leadscrew 63 a of the first focus motor 63 rotates based on a drive signalinput from the focus drive controller 41. Rotation generated by thefirst focus motor 63 is converted into a translatory movement of thesecond lens group supporting frame 53 to the Z axis direction by thelead screw 63 a and the first rack 58, and the second lens groupsupporting frame 53 can transfer to the Z axis direction.

The second focus regulating unit 73 has the second focus motor 64, thefocus drive controller 41 and the second photosensor 67. The secondfocus motor 64 is on a side closer to the imaging surface than thediaphragm unit 62, and is fixed to the fixing frame 50. The second focusmotor 64 drives the fourth lens group supporting frame 55 to the Z axisdirection. The lead screw 64 a of the second focus motor 64 rotatesbased on a drive signal input from the focus drive controller 41.Rotation generated by the second focus motor 64 is converted into atranslatory movement of the fourth lens group supporting frame 55 to theZ axis direction by the lead screw 64 a and the second rack 59, so thatthe fourth lens group supporting frame 55 can transfer to the Z axisdirection.

The third focus regulating unit 74 has the third focus motor 65, thefocus drive controller 41 and the third photosensor 68. The third focusmotor 65 is on a side closer to the imaging surface than the diaphragmunit 62, and is fixed to the guide pole supporting frame 51. The thirdfocus motor 65 drives the fifth lens group supporting frame 56 to the Zaxis direction. The lead screw 65 a of the third focus motor 65 rotatesbased on a drive signal input from the focus drive controller 41.Rotation generated by the third focus motor 65 is converted into atranslatory movement of the fifth lens group supporting frame 56 to theZ axis direction by the lead screw 65 a and the third rack 60, so thatthe fifth lens group supporting frame 56 can transfer to the Z axisdirection.

The focus drive controller 41 can control all the three focus motors 63,64 and 65 simultaneously at different drive speeds, or can drive onlyany one or two of the focus motors. When the focus lens groups G2, G4and G5 are driven to a focus position, the three focus motors 63, 64 and65 are simultaneously drive so that a speed of an AF operation can beheightened.

The diaphragm regulating unit 75 has the diaphragm unit 62, a diaphragmdrive motor (not shown) for driving the diaphragm unit 62 and adiaphragm drive controller 42 for controlling the diaphragm drive motor.The diaphragm drive motor is, for example, a stepping motor. Thediaphragm drive motor is driven based on a drive signal input from thediaphragm drive controller 42. A driving force generated by thediaphragm drive motor drives a diaphragm blade 62 a to an open directionand a close direction so as to change an open shape. The diaphragm blade62 a is driven so that a aperture value of the optical system L can bechanged.

The shake correcting unit 76 is a unit for repressing a shake of anoptical image caused by movements of the interchangeable unit 2 and thecamera body 3, and has an electromagnetic actuator 46, a positiondetecting sensor 47 and a shake correcting microcomputer 48.

The electromagnetic actuator 46 drives the third lens group supportingframe 54 to a direction perpendicular to the optical axis AZ. That is tosay, the electromagnetic actuator 46 drives the third lens group G3 tothe direction perpendicular to the optical axis AZ. The positiondetecting sensor 47 is a sensor for detecting the position of the thirdlens group supporting frame 54 with respect to the diaphragm unit 62.The interchangeable lens unit 2 is mounted with a movement detectingsensor (not shown) such as a gyro sensor. The shake correctingmicrocomputer 48 controls the electromagnetic actuator 46 based on adetected result of the position detecting sensor 47 and a detectedresult of the movement detecting sensor. As a result, a shake of asubject image caused by the movement of the digital camera 1 can becontrolled.

As a method for repressing a shake of a subject image, en electronicshake correcting method for correcting a shake appearing on an imagebased on image data output from the imaging sensor 11 may be adopted.Further, as a method for repressing a shake of an optical image, asensor shift method for driving the imaging sensor 11 to the twodirections perpendicular to the optical axis AZ may be adopted.

The lens microcomputer 40 has a CPU (not shown), a ROM (not shown) and amemory 40 a. A program stored in the ROM is loaded into the CPU so thatvarious functions can be realized. For example, the lens microcomputer40 can recognize that the second lens group supporting frame is on aposition of the original point based on a detection signal of the firstphotosensor 66.

The memory 40 a is a nonvolatile memory, and can retain information thatis stored even in a state that a power supply is stopped. The memory 40a stores information about the interchangeable lens unit 2 (lensinformation), position information about the focus groups according tosubject distances (information about tracking curves) and the like. Thelens microcomputer 40 controls the focus motors 63, 64 and 65 based onthe position information about the focus groups according to subjectdistances to drive the focus lens groups to the Z axis direction. Thelens microcomputer 40 can obtain the positions of the focus lens groupsG2, G4 and G5 in the direction of the optical axis AZ. That is to say,the lens microcomputer 40 can obtain subject distances. The subjectdistances are distances up to subjects whose optical images are focusedby the optical system L. Concretely, the lens microcomputer 40recognizes that the second lens group supporting frame 53 is in theposition of the original point based on a detection signal of the firstphotosensor 66, and then counts a drive amount of the first focus motor63 (for example, a number of steps) so as to obtain the position of thesecond lens group GP in direction of the optical axis AZ. Further, thelens microcomputer recognizes that the fourth lens group supportingframe 55 is on the position of original position based on a detectionsignal of the second photosensor 67, and then counts a drive amount ofthe second focus motor 64 (for example, a number of steps) so as toobtain the position of the fourth lens group G4 in the direction of theoptical axis AZ. Further, the lens microcomputer 40 recognizes that thefifth lens group supporting frame 56 is on the position of the originalpoint based on a detection signal of the third photosensor 68, and thencounts a drive amount of the third focus motor 65 (for example, a numberof steps) so as to obtain a position of the fifth lens group G5 in thedirection of the optical axis AZ.

1-3. Camera Body

A schematic configuration of the camera body 3 is described withreference to FIGS. 1 to 4. As shown in FIGS. 1 to 4, the camera body 3has a chassis 3 a, the body mount 4, an operating unit 39, an imageobtaining section 35, an image display unit 36, a finder section 38, abody microcomputer 10 and a battery 22.

The chassis 3 a composes an exterior section of the camera body 3. Asshown in FIGS. 4A and 4B, the body mount 4 is provided to a frontsurface of the chassis 3 a, and the operating unit 39 is provided to arear surface and an upper surface of the chassis 3 a. Concretely, adisplay unit 20, a power switch 25, a mode switching dial 26, a crossoperation key 27, a menu setting button 28, a setting button 29, a modeswitching button 34 and a moving image recording operation button 24 areprovided to a rear surface of the chassis 3 a. A shutter button 30 isprovided to an upper surface of the chassis 3 a.

The body mount 4 is a portion to which the lens mount 95 of theinterchangeable lens unit 2 is attached and has a body side contactpoint (not shown) electrically connectable to the lens side contactpoint 91. The camera body 3 can send/receive data to/from theinterchangeable lens unit 2 via the body mount 4 and the lens mount 95.For example, the body microcomputer 10 (described later) sends a controlsignal such as an exposure synchronizing signal to the lensmicrocomputer 40 via the body mount 4 and the lens mount 95.

As shown in FIGS. 4A and 4B, the operation unit 39 has various operationmembers for user's input of operation information. For example, thepower switch 25 is a switch for turning on/off a power supply of thedigital camera 1 or the camera body 3. When the power supply is broughtinto an ON state by the power switch 25, the camera body 3 and theinterchangeable lens unit 2 supplies powers to the respective sectionsof the interchangeable lens unit 2.

The mode switching dial 26 is a dial for switching an operation modeamong a still image recording mode, a moving image recording mode and areproducing mode. The user rotates the mode switching dial 26 to becapable of switching the operation mode. When the still image recordingmode is selected by the mode switching dial 26, the operation mode canbe switched into the still image recording mode. When the moving imagerecording mode is selected by the mode switching dial 26, the operationmode can be switched into the moving image recording mode. The movingimage recording mode basically enables the recording of moving images.Further, when the reproducing mode is selected by the mode switchingdial 26, the operation mode can be switched into the reproducing mode,and captured images can be displayed on the display unit 20.

The cross operation key 27 is a button for enabling a user to select up,down, right and left directions. For example, a desired menu can beselected from various menu screens displayed on the display unit 20 byusing the cross operation key 27.

The menu setting button 28 is a button for setting various operations ofthe digital camera 1. The setting button 29 is a button for determiningexecution of various menus.

The moving image recording operation button 24 is a button forinstructing the start and stop of the recording of moving images. Evenwhen the operation mode selected by the mode switching dial 26 is thestill image recording mode or the reproducing mode, the operation modeshifts to the moving image recording mode forcibly regardless ofcontents set by means of the mode switching dial 26 and the recording ofa moving image is started by pressing down the moving image recordingoperation button 24. Further, when the moving image recording operationbutton 24 is pressed down during the recording of a moving image, therecording of the moving image is completed, and the operation modeshifts to an operation mode selected by the mode switching dial 26,namely, the operation mode before the start of the recording of themoving image. For example, when the still image recording mode isselected by the mode switching dial 26 at the time of pressing themoving image recording operation button 24, after the moving imagerecording button 24 is again pressed down, the operation modeautomatically shift to the still image recording mode.

The shutter button 30 is operated by the user at the time of shooting.When the shutter button 30 is operated, a timing signal is output to thebody microcomputer 10. The shutter button 30 is a two-stage switch forenabling a half-press operation and a full-press operation. When theuser performs the half-press operation, a photometric process and adistance measuring process starts. When the user fully presses theshutter button 30 in a state of the half-press of the shutter button 30,a timing signal is output, and the image obtaining section 35 obtainsimage data.

As shown in FIG. 2, a lens removing button 99 for removing theinterchangeable lens unit 2 from the camera body 3 is provided to thefront surface of the camera body 3. The lens removing button 99 has acontact point (not shown) that is in an ON state when the user pressesdown the lens removing button 99. The lens removing button 99 iselectrically connected to the body microcomputer 10. When the lensremoving button 99 is pressed down, the built-in contact point is turnedON, and the body microcomputer 10 can recognize that the lens removingbutton 99 is pressed down.

The image obtaining section 35 has an imaging sensor 11 such as a CCD(Charge Coupled Device) for making photoelectric conversion, a shutterunit 33 for regulating an exposure state of the imaging sensor 11, ashutter controller 31 for controlling drive of the shutter unit 33 basedon a control signal from the body microcomputer 10, and an imagingsensor drive controller 12 for controlling the operation of an imagingsensor 11.

The imaging sensor 11 is, for example, a CCD (Charge Coupled Device)sensor for converting an optical image formed by the optical system Linto an electric signal. The imaging sensor 11 is controlled to bedriven by a timing signal generated from the imaging sensor drivecontroller 12. The imaging sensor 11 may be a CMOS (Complementary MetalOxide Semiconductor) sensor.

The shutter controller 31 drives a shutter drive actuator 32 accordingto a control signal output from the body microcomputer 10 that hasreceived the timing signal to operate the shutter unit 33.

In the first embodiment, a contrast detecting system that uses imagedata generated by the imaging sensor 11 is adopted as the autofocusingsystem. The use of the contrast detecting system can realize highlyaccurate focus regulation.

The body microcomputer 10 is a control device that controls a center ofthe camera body 3, and controls the respective sections of the digitalcamera 1 according to operation information input into the operationunit 39. Concretely, a CPU, a ROM and a RAM are mounted to the bodymicrocomputer 10. Programs stored in the ROM are loaded into the CPU sothat the body microcomputer 10 can realize various functions. Forexample, the body microcomputer 10 has a function for detectingattachment of the interchangeable lens 2 to the camera body 3, or afunction for obtaining information necessary for controlling the digitalcamera 1, such as focus distance information, from the interchangeablelens unit 2.

The body microcomputer 10 can receive signals of the power switch 25,the shutter button 30, the mode switching dial 26, the cross operationkey 27, the menu setting button 28 and the setting button 29. A memory10 a in the body microcomputer 10 stores various pieces of informationabout the camera body 3. The memory 10 a is a nonvolatile memory, andcan retain the stored information even in a state that the power supplyis stopped.

Further, the body microcomputer 10 periodically generates a verticalsynchronizing signal, and generates an exposure synchronizing signalbased on the vertical synchronizing signal in parallel with thegeneration of the vertical synchronizing signal. Since the bodymicrocomputer 10 recognizes exposure start timing and exposure endtiming based on the vertical synchronizing signal in advance, it cangenerate the exposure synchronizing signal. The body microcomputer 10outputs the vertical synchronizing signal to a timing generator (notshown), and outputs the exposure synchronizing signal to the lensmicrocomputer 40 via the body mount 4 and the lens mount 95 at aconstant cycle. The lens microcomputer 40 obtains position informationabout the second lens group supporting frame 53, the fourth lens groupsupporting frame 55 and the fifth lens group supporting frame 56 insynchronization with the exposure synchronizing signal.

The imaging sensor drive controller 12 generates a reading signal of theimaging sensor 11 and an electronic shutter drive signal at a constantcycle based on the vertical synchronizing signal. The imaging sensordrive controller 12 drives the imaging sensor 11 based on the readingsignal and the electronic shutter drive signal. That is to say, theimaging sensor 11 reads pixel data generated by a plurality ofphotoelectric converting devices (not shown) present in the imagingsensor 11 into a vertical transfer section (not shown) according to thereading signal.

Further, the body microcomputer 10 controls the focus regulating units72, 73 and 74 via the lens microcomputer 40.

The image signal output from the imaging sensor 11 is sequentially sentfrom an analog signal processor 13 to an A/D converter 14, a digitalsignal processor 15, a buffer memory 16 and an image compressor 17 to beprocessed. The analog signal processor 13 executes an analog signalprocess such as a gamma process on the image signal output from theimaging sensor 11. The A/D converter 14 converts an analog signal outputfrom the analog signal processor 13 into a digital signal. The digitalsignal processor 15 executes a digital signal process such as noiseremoval and contour enhancement on the image signal converted into thedigital signal by the A/D converter 14. The buffer memory 16 is a RAM(Random Access Memory), and temporarily stores an image signal. Theimage signal stored in the buffer memory 16 is sequentially sent fromthe image compressor 17 to an image recording unit 18 and is processed.The image signal stored in the buffer memory 16 is read by a command ofan image recording controller 19 and is sent to the image compressor 17.The data about the image signal sent to the image compressor 17 iscompressed into an image signal according to a command of the imagerecording controller 19. The image signal has a data size smaller thanthat of the original data due to this compressing process. As the methodfor compressing an image signal, for example, a JPEG (Joint PhotographicExperts Group) system for compressing each image signal of one frame isused. Thereafter, the compressed image signal is recorded in the imagerecording unit 18 by the image recording controller 19. When a movingimage is recorded at this time, the JPEG system for compressing aplurality of image signals per frame can be used. Further, an H.264/AVCsystem for converting image signals of a plurality of framescollectively can be also used.

The image recording unit 18 relates the image signal to predeterminedinformation to be recorded so as to create a still image file or amoving image file based on a command of the image recording controller19. The image recording unit 18 records the still image file or themoving image file based on a command of the image recording controller19. The image recording unit 18 is, for example, an internal memoryand/or a removable memory to be detachable. The predeterminedinformation to be recorded together with the image signal includes adate of recording of an image, focus distance information, shutter speedinformation, aperture value information and recording mode information.The still image file has, for example, an Exif (registered trade name)format or a format similar to the Exif format. Further, the moving imagefile has, for example, an H.264/AVC format or a format similar to theH.264/AVC format.

The image display unit 36 has the display unit 20 and the image displaycontroller 21. The display unit 20 is, for example, a liquid crystalmonitor. The display unit 20 displays the image signal recorded in theimage recording unit 18 or the buffer memory 16 as a visible image basedon a command and from the image display controller 21. As a displayformat on the display unit 20, a display format for displaying only animage signal as a visible image and a display format for displaying animage signal and information at the time of shooting as a visible imageare considered.

The finder section 38 has a liquid crystal finder 8 for displaying animage obtained by the imaging sensor 11, and a finder window 9 providedto the rear surface of the chassis 3 a. The user peers through thefinder window 9 to be capable of visually recognizing an image displayedon the liquid crystal finder 8.

The battery 22 supplies powers to the respective sections of the camerabody 3, and further supplies a power to the interchangeable lens unit 2via the lens mount 95. In the first embodiment, the battery 22 is arechargeable battery. The battery 22 may be a dry cell or an externalpower supply for externally supplying a power through a power cord.

1-4. Correspondence Relationship with the Present Invention

The fourth lens group (main group focus lens) G4 is one example of afirst focus lens. A configuration composed of the second lens group G2and the fifth lens group G5 (sub group focus lenses) is one example ofsecond focus lenses. The body microcomputer 10 is one example of adetermining unit. The focus lens drive controller 41, the diaphragmdrive controller 42 or the lens microcomputer 40 is one example of acontrol unit. A configuration composed of the main group focus lens G4,the sub group focus lenses G2 and G5, the focus lens drive controller41, the lens microcomputer 40 and the body microcomputer 10 is oneexample of the focusing system. The digital camera 1 is one example ofthe image-capturing device.

In the following description, the configuration composed of the firstfocus lens, the second focus lens, the focus lens drive controller 41,the lens microcomputer 40 and the body microcomputer 10 is called thefocusing system as the need arises.

2. Operation

An operation of the digital camera 1 according to the first embodimentis described below.

2-1. Recording Mode

The digital camera 1 has two recording modes. Concretely, the digitalcamera 1 has “a finder recording mode” for enabling the recording whilethe user is observing a subject through the finder window 9, and “amonitor recording mode” for enabling the recording while the userobserving a subject on the display unit 20.

In the finder recording mode, for example, the image display controller21 drives the liquid crystal finder 8. As a result, an image of thesubject obtained by the imaging sensor 11 (so-called a through image) isdisplayed on the liquid crystal finder 8.

In the monitor recording mode, for example, the image display controller21 drives the display unit 20, so that real-time image of the subject isdisplayed on the display unit 20. The changeover between the tworecording modes is carried out by the recording mode switching button34.

2-2. Recording of Still Image

When the shutter button 30 is pressed fully by the user, a command issent from the body microcomputer 10 to the lens microcomputer 40 to setthe aperture value of the optical system L is set to an aperture valuecalculated based on an optical measured output from the imaging sensor11. The lens microcomputer 40 controls the diaphragm drive controller 42to control the diaphragm unit 62 to obtain the instructed aperturevalue. Simultaneously with the instruction of the aperture value, adrive command is sent from the imaging sensor drive controller 12 to theimaging sensor 11, and a drive command of the shutter unit 33 is sent.The imaging sensor 11 is exposed by the shutter unit 33 only for a timeof the shutter speed calculated based on the optical measured outputfrom the imaging sensor 11.

When an operation mode of the shake correcting unit 76 is ON, the shakecorrecting unit 76 performs a shake correcting operation, describedlater, at least while the imaging sensor 11 is being exposed.

The body microcomputer 10 executes a process for capturing an image, andwhen the capturing is completed, it sends a control signal to the imagerecording controller 19. The image recording unit 18 records the imagesignal in the internal memory and/or the removable memory based on acommand from the image recording controller 19. The image recording unit18 records information about the recording mode (whether the autofocusrecording mode or the manual focus recording mode) as well as the imagesignal in the internal memory and/or the removable memory based on acommand from the image recording controller 19.

Further, after the completion of the exposure, the imaging sensor drivecontroller 12 reads image data from the imaging sensor 11, and performsa predetermined image process. Then the image data is output to theimage display controller 21 via the body microcomputer 10. As a result,an captured image is displayed on the display unit 20.

Further, after the completion of the exposure, the body microcomputer 10resets the shutter unit 33 to an initial position. Further, the bodymicrocomputer 10 provides a command for resetting the diaphragm unit 62to the open position to the diaphragm drive controller 42 in the lensmicrocomputer 40, and the lens microcomputer provides a reset command tothe respective units. After the completion of the resetting, the lensmicrocomputer 40 informs the body microcomputer 10 of the completion ofthe resetting. After reception of information about the reset completionfrom the lens microcomputer 40 and after completion of a series of theprocess after the exposure, the body microcomputer 10 checks that theshutter button 30 is not pressed down, and ends a recording sequence.

2-3. Recording of Moving Image

The digital camera 1 also has a function for recording moving images. Inthe moving image recording mode, the imaging sensor 11 generates imagedata at a constant cycle, and continuously carries out autofocusaccording to the contrast detecting system using the generated imagedata. In the moving image recording mode, when the shutter button 30 ispressed down or the moving image recording operation button 24 ispressed down, a moving image is recorded in the image recording unit 18.Thereafter, when the shutter button 30 or the moving image recordingoperation button 24 is again pressed down, the recording of the movingimage is stopped.

When the operation mode of the shake correcting unit 76 is ON, the shakecorrecting unit 76 performs a shake correcting operation (describedlater) at least while a moving image is being recorded.

2-4. Shake Correcting Operation

A shake to be added to the digital camera 1 is detected by a shakedetecting section. The shake detecting section has a first angularvelocity sensor for detecting a shake in a pitching direction (Ydirection) and a second angular velocity sensor for detecting a shake ina yawing direction (X direction). A shake correcting microcomputer 48performs time integration to output signals obtained from the firstangular velocity sensor and the second angular velocity sensor, andconverts it into shake angle information about the pitching directionand the yawing direction of the digital camera 1. The shake correctingmicrocomputer 48 calculates target position information about the thirdlens group G3 for returning the transfer of an optical image on theimaging surface caused by the shake of the digital camera 1 to itsoriginal position based on the shake angle information. In order totransfer the third lens group G3 according to the target positioninformation, the shake correcting microcomputer 48 computes a differencebetween the target position information and current position informationof the third lens group G3 detected by the position detecting sensor 47,and sends a signal to a pitch actuator (not shown) and/or a yokeactuator (not shown).

The pitch actuator and/or the yoke actuator drive the third lens groupG3 based on this signal. In such a manner, the shake of a subject imagecaused by the shake of the digital camera 1 is corrected.

2-5. Autofocus Operation

The autofocus operation of the digital camera 1 according to the firstembodiment is described below with reference to the drawings.

FIG. 11 is a diagram illustrating a lens positional relationship betweenthe fourth lens group (hereinafter, “main group focus lens”) G4 and thesecond and fifth lens groups (hereinafter, “sub group focus lenses”) G2and G5 of the digital camera 1. The position of the sub group focuslense G2 or G5 with respect to the position of the main group focus lensG4 is a “tracking position”. When the respective lenses are on thetracking positions, the most suitable optical performance and imagequality can be obtained. Further, to shift position of each of the subgroup focus lenses G2 and G5 according to the tracking positioncorresponding to the position of the main group focus lens G4 is“tracking drive”.

In the autofocus mode, when the user operates the shutter button 30, therespective focus lens groups G4, G2 and G5 transfer so as to be focusedon a subject. In this embodiment, the autofocus detection is carried outby a hill climbing system using a captured image.

In the hill climbing system using the captured image, a contrast value(evaluation value) is calculated based on the captured image, and thecontrast value is evaluated so that a focus position (or a focusposition candidate) is detected. To drive the main group focus lens fordetecting the focus position is “scan drive”. In the scan drive, themain group focus lens is driven at a constant speed. The reason fordriving at the constant speed is to obtain the contrast value on lenspositions at equal intervals to improve detection accuracy of the focusposition in the hill climbing system. Further, this is to simplify thelens control. At this time, in a conventional technique, the sub groupfocus lenses are driven by the tracking drive according to the drive ofthe main group focus lens.

FIG. 12A is a diagram describing a movement of the sub group focuslenses in the autofocus operation according to the hill climbing systemwhen performing tracking drive on the lenses. FIG. 12B is a diagramdescribing the lens positions that temporarily changes according to theoperation shown in FIG. 12A. As shown by a straight line in FIG. 12B,the main group focus lens is driven at the constant speed, and the subgroup focus lenses are driven by the tracking drive according to thedrive of the main group focus lens as shown by a broken line of FIG.12B. Concretely, the positions of the sub group focus lenses (trackingpositions) are obtained according to a tracking curve at everypredetermined control zone, and the sub group focus lenses are driven tothe respective tracking positions. That is to say, in the conventionaltechnique, since the sub group focus lenses are not driven at a constantspeed as shown by the broken line of FIG. 12B, noises are generated andtones change at the time of a change in the speed, thereby deterioratingthe sound quality. Further, when the drive speed matches with aresonance speed, the noises become more loud occasionally.

Conventional cameras focused on still images, and thus noises caused bythe lens drive was not really acknowledged as a problem. However,cameras that focus on moving images and enable the autofocus during therecording of moving images have been developed recently, and thus adeterioration in the sound quality due to the noises becomes a problem.In order to avoid such a problem, a method for prohibiting the autofocusduring the recording of moving images may be considered, but this methodcannot sufficiently fulfill users' requirements.

The autofocus operation of the digital camera 1 according to the firstembodiment that solves the above sound problem is described below. FIG.13 is a diagram describing the movements of the main group focus lens G4and the sub group focus lenses G2 and G5 in the focus operation of thedigital camera 1 according to the first embodiment. In this drawing, asolid line shows the movement of the main group focus lens, and a brokenline shows the movement of the sub group focus lenses.

In the scan drive by the main group focus lens G4, it is sufficient onlyto detect whether the focus position is on a Far side or a Near sideuntil a peak (focus position) is detected. That is to say, in the scandrive, it is sufficient only to detect a direction of the focus positionof the optical system with respect to a current position of the maingroup focus lens G4, and the detection accuracy does not have to behigh. Therefore, in the scan drive according to the first embodiment, asshown in FIG. 13, the focus lens drive controller 41 prevents the subgroup focus lenses G2 and G5 from being driven by the tracking drivewith respect to the main group focus lens G4. Hereinafter, such drive iscalled “silent drive”. The silent drive of the sub group focus lenses G2and G5 is concretely to drive at constant-speed. The constant speed is adrive speed at which the most silent drive is enabled in view of a focuslens unit movable together with an actuator, and is set to a speedavoiding a resonance drive speed. In order to further improve thesilence ability and the sound quality, the focus lens drive controller41 may drive the sub group focus lenses G2 and G5 by means ofacceleration and deceleration speed control. For example, when the maingroup focus lens G4 is moved towards the focus position, the sub groupfocus lenses G2 and G5 are accelerated smoothly at start of the driveand then driven at the constant speed. The speed may be reduced justbefore stop.

In the above scan drive, when the sub group focus lenses are driven atthe constant speed, noises and the change in tone caused by switching ofthe speed can be reduced, thereby preventing the deterioration in thequality of recorded sounds while suppressing sound (noise) generation.

In an example of FIG. 13, rescan (after the peak of the evaluation valueis detected, the peak is detected again) is not carried out, but therescan can be carried out in order to increase the detection accuracy.For example, when the focus position (the peak of a mountain) cannot bedetected, the detection accuracy is reduced and the scan speed isheightened so that the approximate focus position (the peak of themountain) is detected. Thereafter, if the focus position can beapproximately detected, the focus accuracy can be improved by the rescanwith the speed being lowered.

During the rescan, in order to further improve the detection accuracy,the sub group focus lenses G2 and G5 may be driven by the trackingdrive. That is to say, when the rescan drive is carried out after thescan drive, the sub group focus lenses G2 and G5 may be driven in thetracking drive with respect to the main group focus lens G4. At thistime, when a difference between the current positions of the sub groupfocus lenses G2 and G5 and the tracking positions of the sub group focuslenses G2 and G5 with respect to the position of the main group focuslens G4 is not less than a predetermined value (influences the detectionaccuracy), the rescan drive does not have to be carried out until thesub group focus lenses G2 and G5 transfer to the tracking positions.Further, when the difference is not more than the predetermined value,the rescan drive may be immediately carried out.

The predetermined value varies according to the recording mode, the setaperture value and the image quality, and is calculated according to arecording state. For example, when the still image recording mode, whenthe open (small) aperture value is set, or when the high quality is set,the focus position should be detected accurately, and thus thepredetermined value is preferably set to a smaller value. On the otherhand, when the moving image recording mode, the large aperture value andthe low image quality are set, the high-accurate detection of the focusposition does not have to be carried out, and the focusing speed isgiven priority. For this reason, the predetermined value is preferablyset to a larger value. That is to say, the predetermined value is set sothat the value set at the time of selecting the still image recordingmode is smaller than the predetermined value set at the time ofselecting the moving image recording mode. Further, the predeterminedvalue is set to a larger value as the diaphragm is changed from the openstate to the narrowed state. Similarly, the predetermined value is setto a larger value as an image quality level is changed from the highquality to low quality. As a result, an optimum focusing performance canbe realized according to the recording state.

Second Embodiment

Another example of the autofocus operation of the digital camera 1 isdescribed with reference to FIG. 14. Since the configuration of thedigital camera according to a second embodiment is similar to that inthe first embodiment, the same reference signs are given and thedescription thereof is omitted.

In FIG. 14, a solid line shows the movement of the main group focuslens, and a broken line shows the movement of the sub group focus lens.In the second embodiment, the focus lens drive controller 41 does notstart a drive of the sub group focus lenses G2 and G5, namely, keepsthem stop, until candidates of the focus positions are found by thedrive of the main-group focus lens G4. As a result, the noises in theentire focusing system are further reduced, and simultaneously the powerconsumption can be reduced.

FIG. 19 is a flowchart illustrating focus detection drive according tothe hill climbing system in the second embodiment. When the detection ofthe focus position by the body microcomputer 10 is started, the focuslens drive controller 41 starts scanning of the focus position by themain group focus lens G4 (S101, S102). At this time, the focus lensdrive controller 41 makes a control to stop the sub group focus lensesG2 and G5 (S103).

The body microcomputer 10 monitors a change in the focus state of asubject image according to the scanning of the focus position by themain group focus lens G4. That is to say, the focus lens drivecontroller 41 repeats this process (S101 to S103) until the bodymicrocomputer 10 detects the peak of a change in the focus state (S104).

When the body microcomputer 10 detects the peak (focus position) of thechange in the focus state (S104), the focus lens drive controller 41drives the sub group focus lenses G2 and G5 to predetermined positionscorresponding to the focus position of the main-group focus lens G4(S105, S106).

When the sub group focus lenses G2 and G5 transfer to the predeterminedpositions (S106), the rescan drive is carried out (S107). During therescan drive, the main group focus lens G4 is driven and the sub groupfocus lenses G2 and G5 are driven by the tracking drive with respect tothe main group focus lens G4 (S108, S109). At this time, when thedifference between the current positions of the sub group focus lensesG2 and G5 and their tracking positions with respect to the main groupfocus lens is a predetermined or more value (the detection accuracy isinfluenced), the rescan drive may be stopped until the sub group focuslenses G2 and G5 are driven to the tracking positions. Further, when thedifference is the predetermined or less value, the rescan drive may beimmediately carried out. Since the details of the predetermined valueare similar to those in the first embodiment, the description thereof isomitted.

Also at the time of the rescan, the control may be made so that the subgroup focus lenses G2 and G5 stop. In this case, the true focus positioncan be obtained by correcting the focus position calculated based on thecontrast value of an captured image, based on the positionalrelationship between the sub group focus lenses and the main group focuslens (see FIG. 11) with reference to the tracking lens data.

Further, when drive to the focus position is carried out after the finalfocus position is detected (S110), the silent drive is carried outwithout tracking drive of the sub group focus lenses G2 and G5 withrespect to the main group focus lens G4 (S111).

In the digital camera 1 according to the second embodiment, a noise anda tone change caused at the time of switching the speed do not occur,and suppression of sound and the quality of recorded sounds can beimproved.

In the above flow, although the rescan (S107) is carried out, the rescandoes not have to be carried out.

Third Embodiment

A third embodiment describes the focus operation by moving slightlyforward and backward (wobbling) the lens along the optical axis of themain group focus lens. Since the configuration of the digital camera 1according to the third embodiment is similar to that of the digitalcamera 1 according to the first embodiment, the same reference signs aregiven and the description thereof is omitted.

The wobbling is a drive method for driving to move slightly forward andbackward the focus lenses in order to set the in-focus state, and thiscan ensure the in-focus state immediately when a subject transfers.Concretely, the focus lenses are moved forward and backward along theoptical axis from the current lens positions, and directions of thefocus positions (the focus position changes according to the transfer ofthe subject) are detected based on an image captured on the respectivepositions. Then the focus lenses are moved to the detected directions.This operation is continuously repeated so that the focus lenses can bealways controlled to positions close to the focus positions. For thisreason, the in-focus state can be quickly obtained for the transferringsubject. The wobbling is called also as full-autofocus. The wobblingenables the focusing without user's half-pressing of the shutter button,and thus the in-focus state on the subject can be always maintained.This technique is effective particularly at the time of capturing movingimages and is employed in many video cameras. FIG. 15 is a diagramdescribing the movements of the sub group focus lenses driven by thetracking drive with respect to the main group focus lens when the maingroup focus lens is driven to be wobbled. In the drawing, a solid lineshows the movement of the main group focus lens, and a broken line showsthe movements of the sub group focus lenses driven by the tracking drivewith respect to the main group focus lens. The wobbling drive isconducted by the lens microcomputer 40 controlling the focus lens drivecontroller 41 based on a control signal received from the bodymicrocomputer 10.

In the wobbling, the lens should be always moved slightly forward andbackward. For this reason, in the wobbling drive of the focusing systemcomposed of a plurality of focus lens groups such as this system, whenthe sub group focus lenses are driven in the tracking drive with respectto the main group focus lens, noises and power consumption increase. Adrive method for solving this problem at the time of the wobbling driveis described below.

FIG. 16 is a diagram describing the movements of the focus lenses whenthe main group focus lens and the sub group focus lenses are driven tobe wobbled by the control in the third embodiment. In the drawing, asolid line shows the movement of the main group focus lens and a brokenline shows movement of the sub group focus lenses. As shown in FIG. 16,at the time of the wobbling, the focus lens drive controller 41 does notperform the tracking drive for the sub group focus lenses G2 and G5 withrespect to the main group focus lens G4, but performs the silent drivefor the lenses G2 and G5. That is to say, the focus lens drivecontroller 41 drives the sub group focus lenses G2 and G5 at theconstant speed according to a drive state of the main group focus lensG4. That is to say, the sub group focus lenses G2 and G5 transferwithout following the tracking curve. The constant speed is set to adrive speed which is other than the resonance drive speed. In order tofurther improve the silent ability and sound quality, the focus lensdrive controller 41 may drive the sub group focus lenses G2 and G5 bythe accelerated and decelerated speed control.

With the above configuration, the digital camera 1 performs the silentdrive to the sub group focus lenses G2 and G5 (drive at the constantspeed) in the wobbling drive. For this reason, the generation of thenoises and the change in the tone can be reduced, thereby improvingsilent ability and the quality of a recorded sound.

Fourth Embodiment

Another example of the wobbling drive that can reduce the generation ofthe noises and the change in the tone is described.

FIG. 17 is a diagram describing the wobbling drive according to thefourth embodiment. As shown in the drawing in the fourth embodiment, atthe time of the wobbling, while the center position of the main groupfocus lens G4 does not shift (namely, a subject does not transfer), thesub group focus lenses G2 and G5 are stopped. When the center positionof the main group focus lens G4 shifts, the sub group focus lenses G2and G5 are transferred by the silent drive to the tracking positionscorresponding to the center position of the main group focus lens in thewobbling. Since the configuration of the digital camera 1 according tothe fourth embodiment is similar to the case in the first embodiment,the same reference signs are given and the description thereof isomitted.

Only when the center position of the wobbling (the center position ofdrive of moving slightly forward and backward) changes due to thetransfer of a subject, the focus lens drive controller 41 drives the subgroup focus lenses G2 and G5 in the noise reduction state, therebyrealizing the noise reduction and reducing the power consumption.

FIG. 20 is a flowchart illustrating a focus detecting process at thetime of the wobbling drive in the fourth embodiment.

When the detection of the focus position is started by the bodymicrocomputer 10, the focus lens drive controller 41 starts the wobblingof the focus lens (S120). At this time, the focus lens drive controller41 makes a control so as to drive the main group focus lens G4 (S121)and stop the sub group focus lenses G2 and G5 (S122).

When the body microcomputer 10 detects a change in the center position(the focus position) of the wobbling due to the transfer of the subject(S123), the focus lens drive controller 41 drives the main group focuslens G4 to shift the center position of the wobbling (S124). Further,the focus lens drive controller 41 drives the sub group focus lenses G2and G5 to move to the tracking position corresponding to the centerposition of the main group focus lens G4 (S125). That is to say, themain group focus lens G4 is transferred to a direction of the focusposition, and the positions of the sub group focus lenses G2 and G5 arechanged according to a shift of the center position of the main groupfocus lens G4.

At the time of the wobbling drive, only when the center position of themain group focus lens G4 shifts and the difference between the positionsof the sub group focus lenses G2 and G5 and the tracking positions ofthe sub group focus lenses G2 and G5 with respect to the position of themain group focus lens G4 is the predetermined or more value, the subgroup focus lenses G2 and G5 may be transferred to the trackingpositions corresponding to the center position of the wobbling by thesilent drive (see FIG. 18). The predetermined value varies according tothe recording mode, the set diaphragm and the image quality similarly tothe first embodiment, and is set to a value calculated according to therecording state. That is to say, only when it is determined that theimage quality and the detection accuracy of the focus position aredeteriorated if the sub group focus lenses G2 and G5 are nottransferred, the focus lens drive controller 41 may drive the sub groupfocus lenses G2 and G5.

With the above configuration, the digital camera 1 according to thefourth embodiment can reduce the noises and the change in the tone andcan improve the noise reduction and the quality of recorded sounds.

Fifth Embodiment

In the second embodiment, the sub group focus lenses G2 and G5 arestopped until the peak (focus position) of the change in the focus stateis detected, and when the peak (focus position) of the change in thefocus state is detected, the sub group focus lenses G2 and G5 aredriven. On the contrary, in a fifth embodiment, only when the differencebetween the tracking positions of the sub group focus lenses G2 and G5with respect to the current position of the main group focus lens G4 andthe current positions of the sub group focus lenses G2 and G5 is thepredetermined or more value, the silent drive of the sub group focuslenses G2 and G5 are started. The predetermined value is as described inthe first embodiment.

FIG. 21 is a diagram describing movements of the focus lenses in thefifth embodiment. In FIG. 21, a solid line shows the movement of themain group focus lens and a broken line shows the movement of the subgroup focus lenses.

The focus operation of the digital camera 1 according to the fifthembodiment is described below with reference to the drawings. Since theconfiguration of the digital camera 1 according to the fifth embodimentis similar to the case in the first embodiment, the description thereofis omitted.

FIG. 22 is a flowchart illustrating a focus detection driving methodaccording to the hill climbing system according to the fifth embodiment.When the detection of the focus position is started by the bodymicrocomputer 10, the focus lens drive controller 41 starts to scan thefocus position of the main group focus lens G4 (S131, S12). Further, thefocus lens drive controller 41 makes a control to stop the sub groupfocus lenses G2 and G5. The focus lens drive controller 41 determineswhether the difference between the current positions of the sub groupfocus lenses G2 and G5 and the tracking positions of the sub group focuslenses G2 and G5 with respect to the position of the main group focuslens is the predetermined or more value (S133).

When the difference is the predetermined or more value (S133), the focuslens drive controller 41 transfers the sub group focus lenses G2 and G5to the tracking positions by the silent drive (S134). That is to say,the focus lens drive controller 41 drives the sub group focus lenses G2and G5 at the constant speed. The constant speed is as described before.In order to further improve the noise reduction and the sound quality,the focus lens drive controller 41 may drive the sub group focus lensesG2 and G5 by the accelerated and decelerated speed control.

While scanning the focus position of the main group focus lens G4, thebody microcomputer 10 monitors the change in the focus state of asubject image. The body microcomputer 10 repeats the operation flow fromsteps S131 to S134 until it detects the peak (focus position) of thechange in the focus state (S135).

When the body microcomputer 10 detects the peak (namely, the focusposition) of the change in the focus state (S135), it executes thefollowing process.

The lens microcomputer 40 determines whether the difference between thecurrent positions of the sub group focus lenses G2 and G5 and thetracking positions with respect to the position of the main group focuslens is a predetermined or more value (S136). When the lensmicrocomputer 40 determines that the difference is the predetermined ormore value, the focus lens drive controller 41 transfers the sub groupfocus lenses G2 and G5 to the tracking positions by the silent drive(S137).

Thereafter, the focus lens drive controller 41 carries out rescan inorder to recheck the focus position and improve the detection accuracyof the focus position (S138). In the rescan, the main group focus lensG4 is driven at a lower speed. Further, the focus lens drive controller41 drives the sub group focus lenses G2 and G5 with respect to the maingroup focus lens G4 by the tracking drive (S140). The focus lens drivecontroller 41 repeats the process from steps S138 to S140 until the bodymicrocomputer 10 detects the final focus position (S141).

When the final focus position is detected, the focus lens drivecontroller 41 transfers the main group focus lens G4 and the sub groupfocus lenses G2 and G5 to the final focus positions by the silent drive(S142).

With such an arrangement, the digital camera 1 according to the fifthembodiment can reduce the noises and the change in the tone and canimprove the noise reduction and the quality of recorded sounds.

Other Embodiments

The present invention is not limited to the above embodiments and can bevariously modified and changed without departing from the gist of thepresent invention. Further, the above embodiments are substantiallypreferable examples and do not intent to limit the scope of the presentinvention, its applications and usage thereof. That is to say, theconcept in the above embodiments, namely, the control for the main groupfocus lens and the sub group focus lenses can be applied also to thefollowing case.

(1) In the above embodiments, the digital camera can capture a stillimage and a moving image, but may be capable of capturing either one ofstill image and a moving image.

(2) In the above embodiments, the digital camera may be a digital stillcamera, a digital video camera, a mobile telephone with a camera, or aPDA with a camera.

(3) The digital camera 1 does not contain a quick return mirror, but maycontain a quick return mirror like a conventional single-lens reflexcamera.

(4) The configuration of the optical system L is not limited to those inthe above embodiments. For example, the third lens group G3 may becomposed of a plurality of lenses, or the sixth lens group G does nothave to be provided.

(5) In the above embodiments, the operation of the shutter unit 33controls the exposure time of the imaging sensor 11, but the exposuretime of the imaging sensor 11 may be controlled by an electronicshutter.

(6) In the above embodiments, the three focus regulating units areprovided, but any number (two or more) of units may be provided.

(7) The interchangeable lens unit 2 is a single-focus optical system,but it may be a zoom optical system that can change the focus distance.

(8) The first focus motor 63, the second focus motor 64 and the thirdfocus motor 65 are not limited to a stepping motor, but it may beanother actuator. For example, the actuator may be an electromagneticmotor, a voice coil motor, and a vibration actuator using apiezoelectric device, or the like.

(9) The wobbling drive waveform shown in FIGS. 15 to 18 is a trapezoidalwaveform, but it may be a triangular waveform or a sine waveform.Further, the concept in the above embodiments are not limited only tothe contrast autofocus in the hill climbing system, and similarly can beapplied also to autofocus in a phase difference detecting system.

(10) In the above embodiments, the main group focus lens and the subgroup focus lenses are set, but the concept in the embodiments is notlimited to this. That is to say, dependency may not be provided inmovement among a plurality of focus lens groups, and they may be drivenindependently.

(11) The focus lenses described in the above embodiments may becontrolled only in the interchangeable lens 2. In this case, thefunction of the body microcomputer 10 relating to the control of thefocus lenses described in the above embodiments may be realized in theinterchangeable lens 2. For example, the lens microcomputer 40 mayrealize this function. Further, in the above embodiments, the digitalcamera 1 is an interchangeable lens type digital camera, but the conceptin the above embodiments can be applied also to a digital camera(image-capturing device) where a lens and a camera body are integralwith each other (namely, the lens is detachable).

(12) The drive control of the main group focus lens G4 and the sub groupfocus lenses G2 and G5 described in the above embodiments may be made inthe interchangeable lens 2.

(13) The above embodiments also disclose the concept of a focusingsystem having the following configuration.

A) A focusing system containing an optical system including a firstfocus lens and a second focus lens, the optical system moving forwardand backward along an optical axis to regulate a focus state of asubject image, the focusing system including:

a determining unit for periodically detecting the focus state of thesubject image formed via the first focus lens and the second focus lensand comparing detected results to determine a focus position of theoptical system;

a first drive control unit for controlling the first focus lens to movealong the optical axis based on the determined result of the determiningunit so that the subject image is set in an in-focus state;

a second drive control unit for controlling the second focus lens tomove along the optical axis in order to assist regulation of the focusstate of the subject image; and

a control unit for controlling the second drive control unit to drivethe second focus lens at a constant speed until the determining unitdetermines candidate of a focus position of the subject image.

B) A focusing system containing an optical system including a firstfocus lens and a second focus lens, the optical system moving forwardand backward along an optical axis to regulate a focus state of asubject image, the focusing system including:

a determining unit for periodically determining the focus state of thesubject image formed via the first focus lens and the second focus lensand comparing detected results to determine a focus position of theoptical system;

a first drive control unit for controlling the first focus lens to movealong the optical axis based on the determined result of the determiningunit so that the subject image is set in an in-focus state;

a second drive control unit for controlling the second focus lens tomove along the optical axis in order to assist regulation of the focusstate of the subject image by the first focus lens; and

a control unit for controlling the second drive control unit so that thesecond focus lens is not driven until the determining unit determinescandidate of a focus position of the subject image.

C) A focusing system containing an optical system including a firstfocus lens and a second focus lens, the optical system moving forwardand backward along an optical axis to regulate a focus state of asubject image, the focusing system including:

a determining unit for periodically detecting the focus state of thesubject image formed via the first focus lens and the second focus lensand comparing detected results to determine a focus position of theoptical system;

a first drive control unit for controlling the first focus lens to movealong the optical axis based on the determined result of the determiningunit so that the subject image is set in an in-focus state;

a second drive control unit for controlling the second focus lens tomove along the optical axis in order to assist regulation of the focusstate of the subject image by the first focus lens; and

a control unit for controlling the second drive control unit to drivethe second focus lens when a difference between a tracking position ofthe second focus lens with respect to a current position of the firstfocus lens and a current position of the second focus lens is apredetermined or more value.

D) A focusing system containing an optical system including a firstfocus lens and a second focus lens, the optical system moving forwardand backward along an optical axis to regulate a focus state of asubject image, the focusing system including:

a determining unit for periodically detecting the focus state of thesubject image formed via the first focus lens and the second focus lensand comparing detected results to determine a focus position of theoptical system;

a first drive control unit for controlling the first focus lens to moveslightly forward and backward along the optical axis for the determiningunit determining a position where the subject image is in-focus;

a second drive control unit for controlling the second focus lens tomove along the optical axis in order to assist regulation of the focusstate of the subject image by the first focus lens; and

a control unit for controlling the second drive control unit to drivethe second focus lens at a constant speed when the first focus lens isdriven.

E) A focusing system containing an optical system including a firstfocus lens and a second focus lens, the optical system moving forwardand backward along an optical axis to regulate a focus state of asubject image, the focusing system including:

a determining unit for periodically detecting the focus state of thesubject image formed via the first focus lens and the second focus lensand comparing detected results to determine a focus position of theoptical system;

a first drive control unit for controlling the first focus lens to moveslightly forward and backward along the optical axis for the determiningunit determining a position where the subject image is in-focus;

a second drive control unit for controlling the second focus lens tomove along the optical axis in order to assist regulation of the focusstate of the subject image by the first focus lens; and

a control unit for controlling the second drive control unit to drivethe second focus lens at a constant speed after a center position ofmoving the first focus lens slightly forward and backward shifts.

F) A focusing system, including:

a focus lens moving forward and backward along an optical axis toregulate a focus state of a subject image;

a determining unit for periodically detecting the focus state of thesubject image formed via the focus lens and comparing the detectedresults to determine a focus position of the optical system;

a drive control unit for controlling the focus lens to move along theoptical axis based on the determined result of the determining unit sothat the subject image is set in an in-focus state; and

a control unit for controlling the drive control unit to drive the focuslens, by selecting either one of a silent mode for giving preference tosuppression of operation sounds and a high-accuracy mode for givingpriority to accuracy of the determined result according to a progressingstate during the determination of the focus position of the subjectimage by the determining unit.

Industrial Applicability

The focusing system of the present invention can be applied to anyfocusing system that is installed in a digital camera, a camcorder withan autofocus detecting function, and a mobile telephone with a camera.

EXPLANATIONS OF REFERENCE SIGNS

-   1: digital camera-   2: interchangeable lens unit-   3: camera body-   10: body microcomputer-   11: imaging sensor-   20: display unit-   40: lens microcomputer-   41: focus lens drive controller-   42: diaphragm drive controller-   62: diaphragm unit-   63: first focus motor-   64: second focus motor-   65: third focus motor-   L: optical system-   G1: first lens group-   G2: second lens group (sub group focus lens)-   G3: third lens group-   G4: fourth lens group (main group focus lens)-   G5: fifth lens group (sub group focus lens)-   G6: sixth lens group

The invention claimed is:
 1. A focusing system having an optical systemincluding first and second focus lenses for regulating a focus state ofa subject image, the focusing system being capable of performing a focusoperation for automatically controlling the first and second focuslenses on a focus position, the focusing system comprising: a firstdrive unit configured to drive the first focus lens along the opticalaxis; a second drive unit configured to drive the second focus lensalong the optical axis; a determining unit configured to periodicallydetecting detect a focus state of the subject image formed via theoptical system and determine a focus position of the optical systembased on the detected result in the focus operation; and a control unitconfigured to control the first and second drive unit according to aresult of determining the focus position of the optical system by thedetermining unit, wherein: the control unit controls the first driveunit to drive the first focus lens slightly forward and backward alongthe optical axis and controls the second drive unit to drive the secondfocus lens independently of the first focus lens in order to detect afocus state of the subject image by the determining unit in the focusoperation, the second focus lens has tracking positions corresponding topositions of the first focus lens, which provide suitable opticalperformance according to positions of the first focus lens, the controlunit controls the second drive unit to drive the second focus lensindependently of the first focus lens in the focus operation so as notto trace the tracking position corresponding to the position of thefirst focus lens, and when a center position of the first focus lens indriving forward and backward shifts, the control unit controls thesecond drive unit to drive the second focus lens at a constant speed. 2.The focusing system according to claim 1, wherein the control unitcontrols the first drive unit to drive the first focus lens slightlyforward and backward along the optical axis and controls the seconddrive unit to drive the second focus lens at a constant speed, in orderto determine the focus position of the optical system by the determiningunit.
 3. The focusing system according to claim 1, wherein when thecenter position of the first focus lens in driving slightly forward andbackward shifts and a difference between a tracking position of thesecond focus lens with respect to a current position of the first focuslens and a current position of the second focus lens is equal to or morethan a predetermined value, the control unit controls the second driveunit to drive the second focus lens at a constant speed.
 4. The focusingsystem according to claim 3, wherein the focusing system is installed inan image-capturing device for capturing a subject image formed via theoptical system, the predetermined value is set according to a recordingcondition of the image-capturing device.
 5. The focusing systemaccording to claim 4, wherein the recording condition is a modeselection between a still image recording mode and a moving imagerecording mode, the predetermined value set when the still imagerecording mode is selected is set to a smaller value than that set whenthe moving image recording mode is selected.
 6. The focusing systemaccording to claim 4, wherein the recording condition is a level of anopen/close state of a diaphragm included in the optical system, thepredetermined value is set to a larger value as the diaphragm changesfrom the open state into a closed state.
 7. The focusing systemaccording to claim 4, wherein the recording condition is an imagequality level of image data created based on the imaged subject image,the predetermined value is set to be larger as the image quality levelis changed from high image quality into low image quality.
 8. Thefocusing system according to claim 1, wherein the control unit controlsthe second drive unit to drive the second focus lens along the opticalaxis in order to assist the regulation of the focus state of the subjectimage by the first focus lens.
 9. An image-capturing device comprisingthe focusing system according to claim
 1. 10. An interchangeable lensmountable to a camera body, comprising the focusing system according toclaim 1.